1. Field of the Invention
The present invention relates to a rolling bearing and particularly a rolling bearing of home electric appliances, industrial equipment, and the like used in a high-temperature and high-speed rotation. More particularly the present invention relates to a rolling bearing for a motor supporting a rotor thereof and a rolling bearing for electric parts and auxiliary machines of a car such as an alternator, an electromagnetic clutch for a car air conditioner, a fan coupling apparatus, an intermediate pulley, and an electromotive fan motor.
2. Description of Related Art Including Information Disclosed Under 37 CFR§§1.97 and 1.98
The lubricating composition is packed inside rolling bearings to be incorporated in various industrial machines and vehicles to impart lubricity thereto. The lubricating composition is obtained by kneading base oil and a thickener, and an additive as necessary. As the base oil, synthetic lubricating oil such as mineral oil, ester oil, silicone oil, and ether oil is generally used. As the thickener, a metal soap such as lithium soap and urea-based compounds are generally used. As the additive, an antioxidant, a rust proof agent, a metal deactivator, a viscosity index improver, and the like are used as necessary. As the antioxidant, organic zinc compounds such as zinc alkyldithiophosphate and amine compounds such as alkylated diphenylamine are used singly or in combination.
In recent years, rolling bearings for use in home electric appliances and industrial equipment are used in a high-temperature and high-speed rotation and demanded to be excellent in quietness and durability at high temperatures and high speeds. As a lubricating composition such as grease which is excellent in the high-temperature durability, restrains abnormal noise when it is cold, and is excellent in a peeling resistance property at a high temperature and under a high load, a lubricating composition composed of base oil consisting of synthetic hydrocarbon oil and ester oil and a urea-based thickener added to the base oil is known (see patent documents 1 and 2).
As a lubricating composition having a long life until before seizing occurs in a high-temperature and high-speed rotation condition, a composition containing ester oil as its base oil and 3 to 30 wt % of a thickener essentially containing an aliphatic diurea compound (see patent document 3) is known.
A sliding member or a rolling member having a chemical reaction film layer of a compound having a thickness of 0.05 to 0.5 μm formed on the surface thereof by a chemical bond reaction of at least one kind selected from among an organic phosphorus compound, an organic sulfur compound, an organic chlorine compound, and an organic metal compound is known (see patent document 4). A metal material for a bearing having a film of a metal salt of a thiophosphorus acid formed on the surface thereof is also known (see patent document 5).
In recent years, there is a tendency for motors to be made smaller. A bearing supporting the rotor of a motor tends to be operated at a higher speed and under a higher surface pressure. Motors for home electric appliances and equipment for cars are required to be quiet. Motors for industrial machines are required to have high-temperature durability in addition to quietness. Conventionally the grease compositions as described in the patent documents 1 and 2 are mainly used to lubricate rolling bearings for these motors.
Because use conditions such as a high-speed rotation, a high surface pressure have become strict owing to the growing demands for downsizing and high performance, there arises a problem that a peculiar peeling phenomenon occurs with the rolling surface of the bearing turning into white in its texture. Unlike peeling which occurs inside the rolling surface owing to metal fatigue, the peculiar peeling phenomenon is a destructive phenomenon which occurs from the rolling surface at a comparatively shallow portion thereof with the rolling surface turning into white in its texture and is considered a hydrogen brittleness caused by hydrogen generated by the decomposition of grease.
As a method of preventing the peculiar peeling phenomenon which occurs in an early stage with the rolling surface turning into white in its texture, the method of adding the passivating agent to the grease composition (see patent document 6) and the method of adding the bismuth dithiocarbamate thereto are known (see patent document 7).
Owing to a recent growing demand for downsizing of vehicles, weight saving thereof, and the improvement of quietness, attempts are being made to manufacture smaller and more lightweight electric parts and auxiliary parts of a car and make the engine room airtight. On the other hand, there is a growing demand for a high output and a high efficiency for the performance of various apparatuses of the car. Thus the present tendency is to compensate the miniaturization-caused reduction of the output of the electric auxiliary machines of the car provided inside the engine room by rotating them at high speeds. As examples of rolling bearings for use in the electric auxiliary machines of the car, the outline of each of a rolling bearing for a fan coupling apparatus, a rolling bearing for an alternator, a rolling bearing for an idler pulley is described below.
In the fan coupling apparatus, a viscous fluid is sealed inside it. A housing having an air-feeding fan mounted on its peripheral surface is coupled to a rotor directly connected to the engine through a bearing. By utilizing the shear resistance of the viscous fluid which increases and decreases in response to an atmospheric temperature, the amount of a driving torque transmitted from the engine and the number of rotations of the fan are controlled. Thereby the fan coupling apparatus feeds optimum air corresponding to the temperature of the engine. Therefore the rolling bearing for use in the fan-coupling apparatus is demanded to have a high heat resistance, grease-sealing performance, and durability so that the rolling bearing withstands a high rotational speed change in the range from 1000 rpm to 10000 rpm in dependence on a fluctuation of the temperature of the engine and in addition withstands very strict environment in which it is driven in summer at a high speed not less than 10000 rpm at a high temperature not less than 180° C.
The alternator for use in a car receives the rotation of an engine and generates electricity, thus supplying an electric power to an electric load of the car and has a function of charging a battery. Therefore the rolling bearing for use in the alternator is demanded to have a high heat resistance, grease-sealing performance, and durability so that the rolling bearing withstands a very strict environment in which it is rotated at a high speed not less than 10000 rpm at a high temperature not less than 180° C.
The idler pulley of the car is used as a belt tensioner for the driving belt transmitting the rotation of the engine to electric auxiliary machines thereof. The idler pulley has the function of a pulley for imparting a tensile force to the driving belt when the distance between rotating shafts is fixed. The idler pulley has another function of an idler used to change the travel direction of the belt or avoiding interference of obstacles to reduce the volume inside the engine chamber. Therefore the rolling bearing for use in the idle pulley is demanded to have a high heat resistance, grease-sealing performance, and durability so that the rolling bearing withstands a very strict environment in which it is rotated at a high speed not less than 10000 rpm at a high temperature not less than 180° C.
A grease composition is mainly used to lubricate the rolling bearings for use in electric parts and auxiliary machines of the car. Because the use conditions such as a sudden acceleration/deceleration, high-temperature rotation, a high-speed rotation, and the like have become strict, similarly to the rolling bearing for the motor, there arises a problem that the peculiar peeling phenomenon occurs with the rolling surface of the bearing turning into white in its texture. In the rolling bearings, as a method of preventing the peculiar peeling phenomenon which occurs in an early stage with the rolling surface thereof turning into white in its texture, the method of adding the passivating agent to the grease composition (see patent document 6) and the method of adding the bismuth dithiocarbamate thereto are known (see patent document 7) as in the case of the rolling bearing for the motor.